The present invention relates to a high precision voltage-to-current converter, particularly for low supply voltages.
The electronic arts include different fields in which it is necessary to operate with low supply voltages. One of these is the telephonic field, wherein the lower the voltage, the greater the line length with which a circuit can operate.
For such uses it is obviously necessary to have circuits specifically suitable for low voltages.
The present invention is specifically concerned with voltage-to-current converters, which in the prior art were not able to provide the utmost precision for low supply voltages. In particular, there exists a prior art converter which is based on the use of a differential stage with two oppositely arranged transistors with a coupling resistance among the common emitter terminals, wherein the input signal is constituted by a voltage applied between the two bases of the transistors and the output signal is constituted by the current which passes through one of said transistors. The precision of this known converter is poor, primarily because the conversion ratio depends on the sum of non-homogeneous resistances, such as the coupling resistance (of the static kind) on the one hand, and the inner resistances of the two transistors (of the dynamic kind) on the other hand. Any changes of the supply current of the two transistors, comprising corresponding changes of the inner resistances of the same transistors, in turn negatively influence the precision of the conversion ratio.